In general, when making a right/left turn at an intersection, a vehicle needs to use its turn signal lamp at a point within a given reach of the intersection to notify nearby vehicles that the vehicle is going to make the right/left turn at the intersection. It is important for a following vehicle's driver to previously recognize the right/left turn of the preceding vehicle. If the following vehicle's driver can know that the preceding vehicle will make a right/left turn at the intersection, he or she can smoothly pass through the intersection by, for example, changing to another lane.
In some actual cases, however, the turn signal lamp is not always manipulated at a point within a given reach of the intersection. The turn signal lamp may be manipulated immediately before the intersection or may not be manipulated at all even though the vehicle is going to make a right/left turn at the intersection.
In such a case, the following vehicle's driver may miss the timing to change the lane and may not be able to smoothly pass through the intersection, because, for example, he or she has to unnecessarily wait at the back of the preceding vehicle that is going to make a left turn.
As a technique for addressing this difficulty there is proposed a system (e.g., see JP-2002-190092A) that stores a history of right/left turning at intersections and predicts right/left turning of the vehicle before the vehicle pass through the intersection.
The technique described in JP-2002-190092A predicts the right/left turn of the vehicle based on the history of the right/left turn at intersections. However, since no history is available for a newly opened road, the right/left turn of the vehicle cannot be accurately predicted until the elapse of a sufficient amount of time. As a result, immediately after a new road is opened, the technique described in JP-2002-190092A fails to enable the vehicle to smoothly pass through an intersection.